C++ :: Malloc For Union Inside Structure Fails

I have some problem while allocating memory to a union inside structure. Below is the code i am using

ON SYSTEM1:

This works fine

ON SYSTEM2:

compiler complains saying "need structure or union type" while allocating MYSTRUCT1.

If I change:

shreyas[0].UnionAttr.struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)
to
shreyas[0].UnionAttr->struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)

This compiler on SYSTEM2 is happy. but second way does not look correct to me and compiler on system 1 complains about it. Which is the correct way to allocate memory?

If first one is correct then what should i look in for to avoid this error? Could this be an issue with compiler on SYSTEM2? If i use second method on SYSTEM2 code segfaults during malloc.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct mystruct1 {
int a;
int b;

[Code] ....